The present invention relates in general to safety devices for maintaining down hole hydraulically operated apparatus, such as blow out preventers, in operational condition if the connection between the well and marine riser is disconnected or damaged. More specifically, the present invention relates to an improved safety apparatus for automatically sealing hydraulic lines within a sub-sea well head casing when the casing is disconnected from an associated well head connector and Christmas assembly to maintain hydraulic pressure operating the down hole apparatus, i.e. blow out preventer.
In oil well drilling and production operations in both land and sub-sea locations, oil, mud and hydraulic fluids are normally transmitted through tubing, through the tubing-casing annulus and through casing annuli formed between successive generally concentric casings and hydraulic lines. Most often, these fluids are transmitted under very high pressures. It has long been a problem to effectively control the flow of these high pressure fluids through the tubing, tubing-casing, casing-casing annuli and hydraulic lines. The principle solution in the past has been to seal both the tubing and casing strings by two separate sealing elements within a casing head to affect an annulus seal. An access port into the annulus was then provided through the head between the two sealing elements. Fluid flow into or out of the annulus thus sealed off was controlled by means of a valve external of a casing head at the axis port. This prior arrangement presented many problems where the casing head was not readily accessible, particularly in sub-sea oil well drilling and production operations where the casing head may be at the bottom of the sea perhaps hundreds of feet below the floating vessel or platform from which the drilling and production operations are being controlled.
To obviate the problems inherent in a system which utilizes a valve external of the casing head in sub-sea oil well drilling operations where the casing heads is not readily accessible, annulus valve apparatus has been developed which is operable internally within the annuli formed between tubing-casing and casing-casing which was operable between a valve-opened and a valve-closed condition by means of standard wire line tooling which is in common use in the industry. Exemplary of an internal annulus valve apparatus is the annulus valve disclosed in U.S. Pat. No. 3,360,048, Watkins.
The annulus valve of Watkins was very effective in sealing annuli during routine maintenance and production operations of a pre-planned nature. However, due to the requirement that wire line tooling be used to operate the annulus valve, in those instances where the casing string or casing head were severed or damaged there was no provision for automatically sealing the annuli or hydraulic lines to prevent pollution of the environment by escaping fluids from therewithin. This problem was aggravated in sub-sea operations by the movement of the drilling platform or drilling ship and the increased risk of separation at the casing head due to tidal movement.
Of primary importance in sub-sea operations is the control of the various blow-out preventive equipment at or below the casing head. A particularly effective method of operating the various blow-out equipment has utilized pressurized hydraulic control lines which operate the safety equipment between a closed and an opened position. In these cases, due to the very great risk of pollution should the blow-out prevention equipment not operate due to damage of the hydraulic control system, the use of wire line tools to operate a hydraulic line valve has been found to be unacceptable. The hydraulic control lines for sub-sea blow-out prevention equipment must be automatic.
It is, therefore, an object of the present invention to disclose and provide an apparatus for and a method of automatically sealing hydraulic lines within a sub-sea well casing when said casing is disconnected from an associated well head connector and Christmas tree assembly.
It is a further object of the present invention to disclose and provide a control apparatus for closing off the well in the event that an upper portion of the Christmas tree structure is inadvertently damaged or destroyed.
Generally stated, the improved safety apparatus of the present invention includes the provision of a valve means movably mounted in the well casing head in association with hydraulic fluid lines running to down hole apparatus such as blow out preventers. The valve means is moved to a line opening position by the landing of the well head connector assembly on the well head. Means are provided for biasing the valve means to a line closing position so that on removal of the well head connector assembly from the casing head, the valve means closes the sub-sea hydraulic lines with respect to the sea environment at the well head and maintains line pressure required to keep down hole apparatus, i.e. blow out preventers operational.
More specifically the improved safety apparatus of the present invention has mandrel means associated with the well head connector assembly for operating the valve means to valve open position. The valve means is generally coaxially aligned within the casing head for receiving the mandrel means for controlling hydraulic fluid flow through passages in the mandrel, valve means and associated hydraulic lines. The valve means is urged into a valve-opened position automatically by the mandrel means as the well head connector assembly is secured to the well casing head. Bias means associated with the valve means urges the valve into a valve-closed position to seal the hydraulic lines automatically when the mandrel means is withdrawn from the well head. Seal means are associated with the valve means and the mandrel means to provide a fluid-type seal between the mandrel means and the valve means, between the valve means and the well casing head and between the mandrel means and the well head connector assembly.
Additional objects and advantages of the apparatus and method in accordance with the present invention will become readily apparent to those skilled in the art from a consideration of the following detailed description of an exemplary embodiment of the apparatus and method of the present invention. Reference will be made to the appended sheets of drawings which will first be discussed briefly.